FIELD-ION MICROSCOPY OBSERVATIONS AND ATOMISTIC SIMULATIONS OF RIGID-BODY SHIFTS AT TILT GRAIN BOUNDARIES IN TUNGSTEN

Field-ion microscopy and molecular dynamics simulation were used for the characterization of the translation states at special grain boundaries in tungsten. It is revealed that rigid-body displacement had the component of displacement parallel to the [110] direction equal to 0 or 1 interplanar spacing. Full vectors of lateral shifts are described by broad statistical distribution. The mathematical simulation revealed two mirror-symmetry-breaking lateral translations along the [Formula: see text] direction of the Σ9 grain boundary corresponding to different atomic structures. It is shown that the partial disconnection with the [Formula: see text] Burgers vector can be considered as the elemental carriers of grain-boundary polymorphic transformation.

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The Microchemistry of Grain Boundaries in Ni3Al

MRS Proceedings ◽

10.1557/proc-133-155 ◽

1988 ◽

Vol 133 ◽

Cited By ~ 10

Author(s):

D. N. Sieloff ◽

S. S. Brenner ◽

Hua Ming-Jian

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

Atom Probe ◽

High Concentration ◽

Field Ion Microscopy ◽

Boron Clusters ◽

Ion Microscopy

ABSTRACTGrain boundary regions in B-doped as well as B-free Ni3AI were studied by field-ion microscopy and atom probe microanalysis. In the ductile, recrystallized, Ni-rich alloys the segregation of boron was often accompanied by an enrichment of nickel. Such an enrichment was not observed at boundaries in B-free alloys. Boron was also observed to segregate to the boundaries in a 25.2A1 - IB alloy which was reported to contain boron clusters. Such clusters were not observed, instead a high concentration of boron pairs were found.

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Atomic Resolution Studies of Tilt Grain Boundaries in NiO

MRS Proceedings ◽

10.1557/proc-60-227 ◽

1985 ◽

Vol 60 ◽

Cited By ~ 2

Author(s):

K. L. Merkle ◽

J. F. Reddy ◽

C. L. Wiley ◽

David J. Smith ◽

G. J. Wood

Keyword(s):

Electron Microscopy ◽

Grain Boundary ◽

Grain Boundaries ◽

Mirror Symmetry ◽

High Resolution Electron Microscopy ◽

Atomic Resolution ◽

High Angle ◽

Structural Units ◽

Atomic Structures ◽

Resolution Electron

AbstractThe atomic structures of a number of <001> high-angle tilt grain boundaries in NiO have been studied by high-resolution electron microscopy (HREM). Crystal 1inity is always maintained right up to the grain boundary (GB). Grain boundary planes bounded by a (100)-plane are preferred, however symmetrical facets are also found at each misorientation. A tendency to match atomic planes across the GB is not only observed in symmetrical, but also in asymmetrical GBs. Structural units can be clearly recognized in symmetrical GBs. Contrast differences suggest that a multiplicity of structural units exists for some GB configurations. Frequently symmetric GBs also show deviations from mirror symmetry. Multislice simultations indicate that the image contrast associated with HREM GB images is not particularly sensitive to GB relaxation.

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Characterization of Internal Interfaces by Atom Probe Field Ion Microscopy

MRS Proceedings ◽

10.1557/proc-295-247 ◽

1992 ◽

Vol 295 ◽

Cited By ~ 1

Author(s):

M. K. Miller ◽

Raman Jayaram

Keyword(s):

Grain Boundaries ◽

Compositional Analysis ◽

Atom Probe ◽

Probe Field ◽

Field Ion Microscopy ◽

Surrounding Matrix ◽

Wide Range ◽

Ion Microscopy ◽

Field Ion Microscope

AbstractThe near atomic spatial resolution of the atom probe field ion microscope permits the elemental characterization of internal interfaces, grain boundaries and surfaces to be performed in a wide variety of materials. Information such as the orientation relationship between grains, topology of the interface, and the coherency of small precipitates with the surrounding matrix may be obtained from field ion microscopy. Details of the solute segregation may be obtained at the plane of the interface and as a function of distance from the interface for all elements simultaneously from atom probe compositional analysis. The capabilities and limitations of the atom probe technique in the characterization of internal interfaces is illustrated with examples of grain boundaries and interphase interfaces in a wide range of materials including intermetallics, model alloys, and commercial steels.

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Atomic Scale Analysis of Cubic Zirconia Grain Boundaries

MRS Proceedings ◽

10.1557/proc-589-323 ◽

1999 ◽

Vol 589 ◽

Author(s):

E.C. Dickey ◽

X. Fan ◽

M. Yong ◽

S.B. Sinnott ◽

S.J. Pennycook

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

Mirror Symmetry ◽

Fluorite Structure ◽

Atomic Scale ◽

Contrast Imaging ◽

Cubic Zirconia ◽

Atomic Structures ◽

Periodic Arrays ◽

Z Contrast

AbstractThe core structures of two symmetric tilt [001” grain boundaries in yttria- stabilized cubic zirconia are determined by Z-contrast imaging microscopy. In particular, near-σ=13 (510) and σ=5 (310) boundaries are studied. Both grain boundaries are found to be composed of periodic arrays of basic grain-boundary structural units, whose atomic structures are determined from the Z-contrast images. While both grain boundaries maintain mirror symmetry across the boundary plane, the 36° boundary is found to have a more compact structural unit than the 24° boundary. Partially filled cation columns in the 24° boundary are believed to prevent cation crowding in the boundary core. The derived grain boundary structural models are the first developed for ionic crystals having the fluorite structure

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On the Shape of Field-Ion Emitters

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100092566 ◽

1976 ◽

Vol 34 ◽

pp. 520-521

Author(s):

H.C. Eaton ◽

B.N. Ranganathan ◽

T.W. Burwinkle ◽

R. J. Bayuzick ◽

J.J. Hren

Keyword(s):

Grain Boundary ◽

Spherical Shape ◽

Theoretical Strength ◽

Evaporation Process ◽

Field Evaporation ◽

Geometric Information ◽

Field Ion Microscopy ◽

Considerable Error ◽

True Shape ◽

Ion Microscopy

The shape of the emitter is of cardinal importance to field-ion microscopy. First, the field evaporation process itself is closely related to the initial tip shape. Secondly, the imaging stress, which is near the theoretical strength of the material and intrinsic to the imaging process, cannot be characterized without knowledge of the emitter shape. Finally, the problem of obtaining quantitative geometric information from the micrograph cannot be solved without knowing the shape. Previously published grain-boundary topographies were obtained employing an assumption of a spherical shape (1). The present investigation shows that the true shape deviates as much as 100 Å from sphericity and boundary reconstructions contain considerable error as a result.Our present procedures for obtaining tip shape may be summarized as follows. An empirical projection, D=f(θ), is obtained by digitizing the positions of poles on a field-ion micrograph.

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Grain Boundary Atomic Structures in SrTiO3 and BaTiO3

Materials Science Forum ◽

10.4028/www.scientific.net/msf.558-559.851 ◽

2007 ◽

Vol 558-559 ◽

pp. 851-856 ◽

Cited By ~ 1

Author(s):

Takahisa Yamamoto ◽

Teruyasu Mizoguchi ◽

S.Y. Choi ◽

Yukio Sato ◽

Naoya Shibata ◽

...

Keyword(s):

Grain Boundary ◽

Grain Boundaries ◽

Annealing Temperature ◽

Unit Length ◽

Rate Dependency ◽

Atomic Structures ◽

Current Voltage ◽

Single Grain ◽

Current Voltage Characteristics ◽

Theoretical Results

SrTiO3 bicrystals with various types of grain boundaries were prepared by joining two single crystals at high temperature. By using the bicrystals, we examined their current-voltage characteristics across single grain boundaries from a viewpoint of point defect segregation in the vicinity of the grain boundaries. Current-voltage property in SrTiO3 bicrystals was confirmed to show a cooling rate dependency from annealing temperature, indicating that cation vacancies accumulate due to grain boundary oxidation. The theoretical results obtained by ab-initio calculation clearly showed that the formation energy of Sr vacancies is the lowest comparing with Ti and O vacancies in oxidized atomosphere. The formation of a double Schottky barrier (DSB) in n-type SrTiO3 is considered to be closely related to the accumulation of the charged Sr vacancies. Meanwhile, by using three types of low angle boundaries, the excess charges related to one grain boundary dislocation par unit length was estimated. In this study, we summarized our results obtained in our group.

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Nanometer Scale Tomographic Investigation of Fine Scale Precipitates in a CuFeNi Granular System by Three-Dimensional Field Ion Microscopy

Microscopy and Microanalysis ◽

10.1017/s1431927612000517 ◽

2012 ◽

Vol 18 (5) ◽

pp. 1129-1134 ◽

Cited By ~ 3

Author(s):

Sophie Cazottes ◽

François Vurpillot ◽

Abdeslem Fnidiki ◽

Dany Lemarchand ◽

Marcello Baricco ◽

...

Keyword(s):

Three Dimensional ◽

Precise Determination ◽

Atomic Scale ◽

Granular System ◽

Field Ion Microscopy ◽

Mean Diameter ◽

The Matrix ◽

The Mean ◽

Ion Microscopy

AbstractThe microstructure of Cu80Fe10Ni10 (at. %) granular ribbons was investigated by means of three-dimensional field ion microscopy (3D FIM). This ribbon is composed of magnetic precipitates embedded in a nonmagnetic matrix. The magnetic precipitates have a diameter smaller than 5 nm in the as-spun state and are coherent with the matrix. No accurate characterization of such a microstructure has been performed so far. A tomographic characterization of the microstructure of melt spun and annealed Cu80Fe10Ni10 ribbon was achieved with 3D FIM at the atomic scale. A precise determination of the size distribution, number density, and distance between the precipitates was carried out. The mean diameter for the precipitates is 4 nm in the as-spun state. After 2 h at 350°C, there is an increase of the size of the precipitates, while after 2 h at 400°C the mean diameter of the precipitates decreases. Those data were used as inputs in models that describe the magnetic and magnetoresistive properties of this alloy.

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Simulation of the interaction of plastic zone dislocations with the grain boundary at brittle-plastic transition temperatures in molybdenum

Uspihi materialoznavstva ◽

10.15407/materials2021.03.066 ◽

2021 ◽

Vol 2021 (3) ◽

pp. 77-85

Author(s):

K. M. Borysovska ◽

◽

N. M. Marchenko ◽

Yu. M. Podrezov ◽

S. O. Firstov ◽

...

Keyword(s):

Fracture Toughness ◽

Grain Size ◽

Grain Boundary ◽

Plastic Zone ◽

Grain Boundaries ◽

Crack Tip ◽

Dynamics Simulation ◽

Density Of Dislocations ◽

Grain Sizes ◽

Pile Up

The (DD) method was used to model the formation of the plastic zone of the top of the cracks in polycrystalline molybdenum. Special attention was paid to take into account the interaction of dislocations in the plastic zone with grain boundaries. Structural sensitivity of fracture toughness was analyzed under brittle-ductile condition. Simulations were performed for a range of grain sizes from 400 to 100 μm, at which a sudden increase in fracture toughness with a decrease of grain size was experimentally shown. We calculated the value of K1c taking into account the shielding action of dislocations. The position of all dislocations in the plastic zone at fracture moment was calculated. Based on these data, we obtained the dependences of dislocation density on the distance from the crack tip thereby confirming significant influence of the grain boundaries on plastic zone formation. At large grain sizes, when the plastic zone does not touch the boundary, the distribution of dislocations remained unchanged. As grains reduce their size to size of the plastic zone, they start formating a dislocation pile – up near the boundaries. Dislocations on plastic zone move slightly toward the crack tip, but the density of dislocations in the middle of the grain remains unchanged, and fracture toughness remains almost unchanged. Further reduction of the grain size leads to the Frank-Reed source activation on the grain boundary Forming dislocation pile-up of the neighbor grains. Its stress concentration acts on dislocations of the first grain and causes redistribution of plastic zone dislocations. If the reduction in grain size is not enough to form a strong pile-up, density of dislocations on plastic zone increases slightly and crack resistance increases a few percent. Further reduction of grains promotes strong pile-up, dislocations move to crack tip, and its density on plastic zone increases. Crack is shielded and fracture toughness increases sharply. The calculation showed that the fracture toughness jump is observed at grain sizes of 100—150 μm, in good agreement with the experiment. Keywords: dislocation dynamics simulation, molybdenum, fracture toughness, grain size, plastic zone, brittle-ductile transition.

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